1. Field of the Invention
The invention relates to surface processing of a component subjected to direct handling by people, mainly relating to a special coating applied on a surface of a metal chassis used in mobile electronic devices, whereby the temperature of the chassis sensed by touching the chassis is reduced.
In the specification, examples of the surface processing of a component (hereinafter surface coated substrate), particularly a metal chassis used in electronic devices are described. However, the surface coated substrate according to the invention has wide-ranging applications, such as in ranges, metallic protection of cooking utensils, materials used for walls and ceilings in buildings, and other general purposes requiring a surface coated substrate with reduced temperature sensed by touching. The surface coated substrate does nothavetobemetallic. A material according to the invention is equally effective as surface coated substrate if its thermal conductivity is large. Further, the material is effective in substrates subjected to high-temperature and also for low-temperature.
2. Background Arts
Examples using electronic devices are explained in the related arts.
Methods of dealing with heat and high temperature at the surface of a chassis has become an important topic in view of a recent move towards light-weight (thinner) and densely-coated chassis in mobile devices such as mobile personal computers, mobile telephones, mobile video cameras, electronic notebooks, and the cooling of semiconductor element as well.
Conventionally, a chassis made of a resinous material, such as ABS (acrylonitrile-butadiene styrene copolymer) is used in mobile devices. However, increasingly, metal chassis are being used in an attempt to strengthen the ever thinner chassis and to improve shock resistance. However, a metal chassis cannot handle a surface temperature above 50.degree. C., because that temperature can cause an unpleasant feeling if held in the hand for a prolonged period of time. Therefore, mobile devices require heat control. The reason for the problem is that, when touched, a material with low thermal conductivity, such as conventional ABS (thermal conductivity .lambda.=0.1 W/mK), due to a loss of heat upon contact to the side of lower temperature, the material is cooler than the hand. Therefore, people will not sense a temperature to be hot. On the other hand, using a material with high thermal conductivity, such as aluminum (thermal conductivity .lambda.=220 W/mK), causes a continuous heat flow from the material to the hand that this leads to an uncomfortable sensation, sometimes even to unpleasant feeling. A conventional method which has dealt with the problem is described below.
For example, in the related art 1 shown in FIG. 10, a metal chassis 1 that became hot due to the heat generated from a heating element, such as heating device 3 mounted on a base 2 has attached to it a cloth, like a felt 4, that has a low thermal conductivity to reduce direct heat flow to a hand. As a general example of such product, see Japanese unexamined patent application hei6-296655. There are high temperature areas in sauna interior and the periphery of thermal head in a printer which also use measures to prevent unpleasant feeling.
Besides using a cloth, an insulating material can similarly be attached, and, according to Japanese patent application hei6-26659, the insulating material made of rubber may be used as a handle of grill door, and Japanese patent application hei4-210012 shows an example of attaching a protection sheet made of rubber to a power-supplied heating plate.
For a door handle used in building, Japanese unexamined patent application hei8-74450, provides an example of attaching a mesh material in an attempt to reduce the touching warmth when opening and closing the door in regions of extreme cold and intense heat.
Other than the given examples, for the related art 2 shown in FIG. 11, adhering a transplanting pile 5 to a high-temperature surface of a metal chassis 1 is done generally, and as an applied example of such a product, an iron and heating device are disclosed in the Japanese unexamined patent application hei6-7599.
The related art 3 of FIG. 12 shows a general use of a paint 6 applied to a surface of the metal chassis 1 that can become high in temperature at the surface.
The related art 4 discloses a technique to deal with the high temperature by using a paint with mixed micro-capsules that are thermally expandable. The thermally expandable micro-capsules are foamed by heating them.
For example, Japanese unexamined patent application hei6-99133 discloses a method of forming a film with a grain-like touch. In this method, a thermosetting paint contains 5.about.30 weight % of the thermally expandable micro-capsules in a paint having 70% of solid ingredient and painted to get the grain-like texture. The shell of the thermally expandable micro-capsules soften at a temperature lower than a hardening temperature of a thermosetting resin. A coating step using thermosetting paint is done in a manner to get the grain-like texture, and this is dried by baking. During baking, the micro-capsules become ruptured from expansion. Accordingly, the film painted will harden to achieve the grain-like texture.
Further, Japanese unexamined patent application sho62-39674 discloses a method of forming an insulating film with pattern. Paint compositions such as a pigment, a filler and a solvent are contained in a thermal plastic resinous vehicle. 10.about.80 weight % of the micro-capsules are contained in 100 weight % of the thermal plastic resinous vehicle. This paint is applied to surfaces of wall, ceiling and floor. Then the heating apparatus is used to heat the applied surfaces for drying to gain an expansion of the painted film. Accordingly, the insulating film with heated pattern is formed.
Furthermore, according to Japanese unexamined patent application hei2-303573, a method of forming the film having a rough pattern is disclosed. The thermally expandable micro-capsules are dispersed in the paint. The paint becomes hardened at a temperature lower than a foaming temperature of the thermally expandable micro-capsules. The paint may be applied all over or part of the surfaces, then hardened by heat. Then a final paint is applied on top of this layer, then hardened. The rough pattern is achieved by heating the micro-capsules beyond the foaming temperature.
In recent years, particularly for mobile electronic devices represented in the mobile computing, a technique to implement a product with small-size, high-performance and light-weight are the key points. From such background, in mobile computing, a use of metallic substrate formed by die-casting is on an increase, from its excellence in terms of strength against weight. Comparing the metallic substrate with the conventional resinous substrate, the thermal conductivity is 100.about.1000 times greater than that of the metallic substrate. Therefore, the metallic substrate is advantageous for spreading heat.
However, when a person touches the surface of a metallic substrate, the person perceives it to be hotter than the resinous substrate at the same temperature, due to a heat collection effect of the metallic substrate. Especially for mobile computers these days, a way to deal with high temperature of the substrate surface is important, especially a way to deal with locally increased temperature such as the surface close to the CPU (Central Processing Unit) is important.
As described previously, as the method to soften the touching warmth, adhering transplanting piles 5 to a high-temperature surface of a metal chassis 1 is done generally, and as applied examples of such products are the heating device and the thermal head chassis of printer. However, there is a problem with the design/appearance when applying the method of transplanting piles to the electronic device chassis. Likewise, other means to deal with the high temperature is a pasting of resinous sheet, however, this method has even more problems with surface applicability, productivity and design/appearance.
Previously described conventional methods in the related arts 1 and 2 are effective as far as the touching warmth is concerned. However, problem with the method of attaching a rubber or a mesh material to electronic devices that have complex curvatures at the chassis surfaces is its difficulty in fitting them into the given shapes. Likewise, there is a problem with the transplanting method where a difficulty arises in uniformly adhering the fibers to a structurally complex portion of the device. There is also a concern about the limitation on the allowed size and shape of the chassis. Even if this fitting is done satisfactorily, a concern for abrasion or staining remains so that there is no ideal method for the product. The same can be said from the viewpoint of productivity because the manufacturing cost will increase.
In comparing the previously described means with a general coating method for a surface of metal chassis as shown in the related art 3 of FIG. 12, the coating method is reasonable in terms of productivity, design, and cost. However, with the normal coating, the thickness of applied paint (film) is normally about 40 .mu.m that the touching warmth from metallic substrate is not softened. The reduction of touching warmth cannot be expected from the normal coating method.
The related art 4 describes a technique of forming the grain-like touch or the rough pattern that are formed by using the paint containing the thermally expandable micro-capsules and a technique of forming a pattern having a thermal insulating property. Neither of the techniques are aiming for a way to deal with the touching warmth, nor to soften the touching warmth from the metallic substrate.